MENTAL INHERITANCE 463 



Let us be more concrete in this matter. If I catch the drift of 

 biological discussion (a hazardous assumption, it may be, for the lay- 

 man in biology to make), no current and generally accepted doctrine of 

 heredity is able to trace in an unbroken series of structures or events 

 the details of the parental organism through the stages of reproduction 

 to the corresponding details of the offspring. The nuclear and non- 

 nuclear substances that are supposed to represent the " vehicle " of 

 heredity do not, I think (except, perhaps, in a few cases) show varia- 

 tions that represent and correspond to the likeness or difference in given 

 characters as these appear in parent and offspring (e. g., differences in 

 height, in shape of leaf, or in color of hair). If, at some future time, 

 these variations are discovered, then they will, I suppose, represent or 

 correspond to mental as well as physical likeness and difference. At 

 present, however, degree of likeness in blood-relations must be de- 

 rived from description or measurement of corresponding characters or 

 qualities to be observed in succeeding generations. And the point at 

 which we are here aiming is this : the establishment of inheritance of 

 these qualities, whether physical or mental, must, in principle, rest 

 upon one and the same basis. The inheritance of eye-color and the in- 

 heritance of memory-type, the inheritance of an " athletic build " and 

 the inheritance of a bad temper are facts of the same order, and similar 

 methods may be laid under prescription for their establishment. 



The great difficulty lies here: how are the characters, mental 

 and physical, to be conceived? and how are they to be described and 

 measured ? 



We have just seen that upon this question of analysis and measure- 

 ment, quite apart from the problem of mechanism, the schools of evo- 

 lution show wide differences of opinion, the biometrician basing his 

 method upon the doctrine of probabilities and proceeding quantita- 

 tively, the Mendelian basing his method upon the doctrine of unit 

 characters and segregation and proceeding analytically and by distinc- 

 tion of qualities. 



Which of these methods, if either, is psychology to adopt? It 

 happens that psychology has already made a provisional choice; or 

 rather, a choice has been made for her. Biometry has been predom- 

 inantly concerned with human, Mendelism with non-human, inherit- 

 ance. It is scarcely an accident, then, that biometrical methods were 

 the first to exploit the mind of man. As you know, biometry's inspira- 

 tion came from Francis Galton, traveler, explorer, geographer, anthro- 

 pologist, student of evolution, psychology and sociology. The grandson 

 of Erasmus Darwin, a representative therefore of one of the highly 

 gifted strains of English blood, Galton has devoted himself to a quanti- 

 tative study of the inheritance of talent and intellect, and to practical 

 measures for purifying and improving the race. His interests revolve 



